The present invention is generally directed to toner compositions, and more specifically to colored magnetic toner compositions. In one embodiment, the present invention is related to colored, magnetic toner compositions that can, for example, be selected for single component development, and more specifically for a number of known inductive single component development processes. In an embodiment, the present invention relates to toner compositions comprised of a polymer resin or resins, an optional waxy, lubricating or low surface energy substance, a colorless or light colored magnetic material, especially a grayish magnetite, a whitening agent, a color pigment, dye or mixture thereof, and a conductive component comprised of metal oxide, such as, for example, powdered tin oxide or titanium oxide, or a mixture of metal oxides. In one specific embodiment of the present invention, there are provided colored, magnetic toner compositions comprised of a known toner polymer, a waxy, lubricating or low surface energy component, a substantially colorless magnetic material, a whitening agent, a color pigment, and wherein the toner particles are coated with a conductive powdered additive comprised of a conductive metal oxide powder of, for example, tin oxide doped with bismuth. The conductive metal oxide powder may be embedded in the toner's surface to prevent its release therefrom. The aforementioned toner compositions generally can possess a volume resistivity of from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably a volume resistivity of about 10.sup.4 to about 10.sup.6 ohm-cm. This level of toner conductivity is particularly suited for use in a number of inductive single component development systems. In another specific embodiment of the present invention, there is provided a colored, magnetic toner composition comprised of an acrylic, methacrylic, styryl, polyesters, olefinic polymer resin, or the copolymeric derivatives thereof, such as poly(butyl methacrylates), styrene-butyl methacrylate copolymers, polypropylenes, polybutylenes, and the like; and dispersed in the toner polymer a waxy or lubricating material, such as hydrocarbon wax, silicones, fluorinated hydrocarbons, and the like, a substantially colorless or slightly grayish colored magnetic material, a whitener, and colored, other than black, pigment particles; and wherein the toner particles are coated with a conductive powder comprised of certain metal oxides, or mixtures thereof. A further embodiment of the present invention relates to the preparation of conductive powdered metal oxides or mixed oxides, and their application as toner conductivity control and surface release agents.
The metal oxide powders that can be selected preferably possess a primary particle size, or average particle diameter of less than 1,000 Angstroms, and more preferably an average particle diameter of from about 10 to about 1,000 Angstroms. These powders can be optionally treated, preferably surface treated with certain organosilane reagents primarily to improve their powder flow properties. Specifically, the conductive powders can possess a specific resistivity of less than 1,000 ohm-cm, and preferably less than 100 ohm-cm, such that when utilized as toner surface additives in an effective amount of, for example, generally less than 20 weight percent, can impart to the toner a volume resistivity of from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably from about 10.sup.4 to about 10.sup.6 ohm-cm. Examples of advantages associated with the colored, magnetic toner compositions of the present invention in embodiments thereof include brilliant image color and wide color variety; relatively high surface conductivity and thus suitability for use in a number of known inductive single component development systems; excellent image fix; nonagglomerating and excellent shelf like stability of, for example, up to 1 year in some instances; and suitability for use in highlight color reprographic processes, especially xerographic and ionographic imaging and printing processes. Additionally, the use of the aforementioned conductive powders can also enhance the toner powder flow characteristics, thus eliminating if desired the utilization of other additives such as Aerosils, and zinc stearate for surface release and flow properties. Another advantage of the conductive oxide powder is related to its ability to reduce the toner's sensitivity to humidity.
The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic, especially xerographic, and ionographic processes. In one embodiment, the toner compositions can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference U.S. Pat. No. 4,885,220, entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The latent images can then be toned with the relatively conductive toner of the present invention by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure. Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers, such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment, the toner compositions of the present invention can be utilized in xerographic imaging apparatuses wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal or photochemical energy fusing.
Heat and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since, for example, these toner compositions can be fused at room temperature. Cold pressure fixability also enables the machine's instant-on feature and permits the design of compact size high speed printers for space saving considerations. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, the prior art colored toners, particularly colored magnetic toners, usually do not possess sufficiently low volume resistivity of, for example, 10.sup.4 to 10.sup.6 ohm-cm to be useful for inductive single component development; the prior art colored magnetic toners also do not usually offer the desirable color quality or a wide color variety; and they in many instances have poor resistance against image smearing, and poor powder flow characteristics. Also, a number of the prior art magnetic toners, inclusive of black toners, often suffer from the known image ghosting problem when used in the transfix ionographic printers such as the Delphax printers. Additionally, the prior art colored magnetic toners are predominantly insulative in nature or possess very low surface conductivity characteristics of, for example, a volume resistivity in excess of 10.sup.8 ohm-cm; and these low levels of conductivity are not considered effectively suitable for inductive single component development, in particular those development systems that are utilized in the commercial Delphax or Xerox ionographic printers and copiers. Other disadvantages of many of the prior art magnetic toners inclusive of black toners generally have a large amount of loosely held surface additives which tend to separate and release from toner particles causing dirt buildup in the development housing as well as white streaks appearing on prints or copies. These and other disadvantages are eliminated, substantially eliminated, or minimized with the toners of the present invention. More specifically, with the colored magnetic toners of the present invention in embodiments thereof control of the toner surface conductivity, surface additive loading, and toners with excellent color quality can be achieved. Also, with the toners of the present invention, image ghosting can be eliminated, in many instances, primarily because of the utilization of the silane-treated conductive metal oxide powder in some embodiments. Image ghosting, which is one of the common known phenomena in transfix ionographic printing processes, refers to, for example, the contamination of the dielectric receiver by residual toner materials which cannot be readily removed in the cleaning process. The result is the retention of latent images on the dielectric receiver surface after cleaning, and the subsequent unwarranted development of these images. One of the usual causes of image ghosting is related to the use of unsuitable or inferior toner materials leading to their adherence to the dielectric receiver during the image development process.
The following United States patents are mentioned in a patentability search report for patent application U.S. Ser. No. 609,333 (U.S. Pat. No. 5,135,832), the disclosure of which is totally incorporated herein by reference, relating to encapsulated toners, and entitled Colored Toner Compositions; U.S. Pat. No. 4,803,144, which discloses an encapsulated toner with a core containing as a magnetizable substance a magnetite, see Example 1, which is black in color, wherein on the outer surface of the shell there is provided a white electroconductive powder, preferably a metal oxide powder, such as zinc oxide, titanium oxide, tin oxide, silicon oxide, barium oxide and others, see column 3, line 59 to column 4; in column 8 it is indicated that the colorant can be carbon black, blue, yellow, and red; in column 14 it is indicated that the electroconductive toner was employed in a one component developing process with magnetic brush development, thus it is believed that the toner of this patent is substantially insulating; U.S. Pat. No. 4,937,167 which relates to controlling the electrical characteristics of encapsulated toners, see for example columns 7 and 8 wherein there is mentioned that the outer surface of the shell may contain optional surface additives 7, examples of which include fumed silicas, or fumed metal oxides onto the surfaces of which have been deposited charge additives, see column 17 for example; U.S. Pat. No. 4,734,350 which discloses an improved positively charged toner with modified charge additives comprised of flow aid compositions having chemically bonded thereto, or chemically absorbed on the surface certain amino alcohol derivatives, see the Abstract for example; the disclosures of each of the aforementioned patents being totally incorporated herein by reference; and which according to the search report are not significant but may be of some background interest U.S. Pat. Nos. 2,986,521; 4,051,077; 4,108,653; 4,301,228; 4,301,228 and 4,626,487.
In a patentability search report in U.S. Pat. No. 5,104,763 (D/90066), relating to encapsulated toners, the disclosure of which is totally incorporated herein by reference, the following United States Patents were listed: U.S. Pat. No. 4,514,484 directed to a powder suitable for developing latent images comprised of magnetic particles coated with a mixture of a thermoplastic resin and a silane, see for example the Abstract of the Disclosure; note column 3, beginning at line 15, wherein it is indicated that into the organic thermoplastic resin is incorporated a silane selected from those illustrated; also incorporated into the thermoplastic resin are magnetic materials, see column 3, beginning at line 35; U.S. Pat. No. 4,565,773 directed to dry toners surface coated with nonionic siloxane polyoxy alkylene copolymers with a polar end, see the Abstract of the Disclosure; and primarily of background interest U.S. Pat. Nos. 4,640,881; 4,740,443; 4,803,144 and 4,097,404, the disclosures of which are totally incorporated herein by reference.
Toner compositions free of encapsulation are known, which toners can be comprised of polymer particles, pigment particles, including colored pigments, low molecular weight waxes, charge enhancing additives, and other additive components, reference for example U.S. Pat. Nos. 3,590,000; 3,983,045; 4,035,310; 4,298,672; 4,338,390; 4,560,635; 4,952,477; 4,939,061; 4,937,157; 4,904,762 and 4,883,736, the disclosures of each of these patents being totally incorporated herein by reference.
There is a need for colored toner compositions, and in particular colored magnetic toner compositions with many of the advantages illustrated herein. Also, there is a need for pressure fixable colored magnetic toners which can be utilized in transfix development systems. Moreover, there is a need for colored magnetic toners, wherein image ghosting, and the like can be avoided or minimized. Furthermore, there is a need for nonagglomerating colored magnetic toners which possess a long shelf life exceeding, for example, 12 months. Also, there is a need for colored magnetic toners with surface conductivity characteristics having a volume resistivity of, for example, from about 10.sup.3 ohm-cm to about 10.sup.8 ohm-cm, and preferably from about 10.sup.4 ohm-cm to about 10.sup.6 ohm-cm, thus enabling their use in a number of known xerographic, and inductive single component development systems. Furthermore, there is a need for colored magnetic toners with excellent powder flow and surface release properties enabling their selection for use in imaging systems without the use of surface release fluids such as silicone oils to prevent image offsetting to the fixing or fuser roll. Another need resides in the provision of colored magnetic toners that are substantially insensitive to changes in humidity. There is also a need for conductive surface additives which are capable of imparting desirable levels of surface conductivity to colored toners without adversely affecting their image color quality. Another associated need resides in the provision of preparative processes for obtaining conductive powdered metal oxides and mixed oxides, such as, for example, tin oxides, which possess a primary particle diameter of less than about 1,000 Angstroms, and a specific resistivity of less than about 1,000 ohm-cm, and which powders are useful as surface conductivity control and release agents for colored magnetic toner compositions free of encapsulation, which toners are suitable for xerographic development processes.